Nowadays there is a trend of Signaling System 7 (SS7) based telecommunication networks to evolve towards Internet Protocol (IP) based telecommunication networks. This trend comes along with a network architecture comprising host nodes and routers. For example, a host node is embodied as a Mobile Switching Center (MSC)-Server and is configured for connecting a subscriber of the host node with a peer end via one or more routers. Accordingly, new demands are posed to the IP based network regarding failure handling of connectivity failures between a host node and a router, between two routers, and between a router and the peer end, or more generally spoken between two network nodes.
It is known that connectivity between two routers may be supervised by so called routing protocols which generally accomplish failure handling of a connectivity failure between two routers or of one of the two routers by means of rerouting data between the two routers.
The connectivity between a host and a router may be supervised using connectivity supervision protocols such as a Virtual Router Redundancy Protocol (VRRP), a Bidirectional Forwarding Detection (BFD) Protocol, and a Stream Control Transmission Protocol (SCTP).
VRRP is defined, for example, according to RFC 3768, and accomplishes failure handling of a failure of a router by dynamically associating an IP address and a corresponding Media Access Control (MAC) address with a set of routers rather than with an individual router. As long as there is one operative router in the set, the IP and MAC addresses will be available. The VRRP protocol attempts to control which of the routers in the set will take over the IP and MAC addresses at any point in time.
However, the VRRP protocol does not work well in all site topologies, in particular not in those topologies having redundant Ethernet switches. In such topologies, which are typically used in telecommunications networks for redundancy reasons, uni-directional connectivity failure between a host and a router may occur and the VRRP protocol can then lead to identical IP and MAC addresses on different routers. Accordingly, such failure cases may lead to loss of data transmitted between the host and the routers. Further, VRRP represents a protocol supported by routers but not by host nodes such that connectivity failures associated with the host node may not be handled. Further, even if VRRP had been supported by a host node, the latter mentioned drawbacks of VRRP would be still present for failure handling of failures associated with the host node.
BFD is defined, for example, according to http://tools.ietf.org/html/draft-ietf-bfd-base-11, and is a protocol usable for detecting failures in a bidirectional communication path between two communication entities such as a host node and a router. Failure detection comprises detecting failures associated with interfaces of the host node and/or the router, and with connection links between the host node and the router.
However, BFD only provides supervision of an IP connectivity between a host node and a router but does not execute any failure resolution of detected connectivity failures.
SCTP is defined, for example, according to RFC 4960 and is a transfer protocol providing connectivity supervision of sessions between two network entities. Further, SCTP provides connectivity failure handling by means of selecting another session path instead of a failed session path.
However, basing failure handling of connectivity failures in an IP based network on SCTP may be difficult, since availability of session path diversity may not be supported in a large IP network.
Further, there are procedures known regarding the association of an IP address of one network entity with another network entity using an Address Resolution Protocol (ARP) as defined, for example, according to RFC 826.
Gratuitous ARP is a procedure usable for changing the association between an IP address and a MAC address and is executed by a host node. In the absence of VRRP (where IP addresses and MAC addresses are both moved from one interface to another interface) the MAC address is usually not changed (so that the MAC address always identifies an interface) while IP addresses can be moved from one interface to another interface by means of sending gratuitous ARP requests or responses from the interface to which an IP address was moved.
ARP cache expiration is a procedure usable for invalidating a timely limited association in a host node of an IP address of a router with a MAC address of the router, in order to dynamically account for changes within the IP network. In a case in which the association of the IP address of the router with the MAC address of the router may expire in the host node, either the host node or the router may have to resolve the association expiration. For example, the association expiration may be caused in that the IP address of the router may change, the router may fail and accordingly the MAC address of the router may turn invalid, or the connection between the host node and the router may fail.
However, ARP cache expiration may not allow for localizing a connectivity failure between the host node and the router. Further, resolving the association expiration may require network capacities in terms of periodically sending messages between the host node and the router.
Thus, the above mentioned failures handling mechanisms of a connectivity failure between a host node and a router may allow for failure handling of failures associated with the router but not with the host node or a connection link between the host node and the router. Further, a host node in the form of the MSC-S may represent a network entity in the telecommunication network configured for providing data transmissions for a plurality of subscribers, thereby failure handling of connectivity failures particularly associated with the host node may represent an important issue.